This invention relates to an improved appliance timer which uses commercially-available electric switches and can be actuated either manually or by a timing mechanism and which automatically deactuates after a predetermined period of time.
Electric timers are widely used in today's household appliances, for example, coffee makers and clock radios, for automatically turning on the appliance at a predetermined time. A typical timer includes a clock and a three-position selector having the usual "auto", "on" and "off" positions. The appliance can be immediately turned on manually by moving the selector from the "off" to the "on" position, or can be automatically turned on at a preset time by positioning the selector to the "auto" position and setting an indicator hand on the clock to the desired time.
Conventional timers of this type are described in U.S. Pat. Nos. 3,138,674 to Boyles, 3,432,625 to Polonsky et al., and 4,414,439 to Pomponio. The Boyles patent shows a conventional clockwork mechanism comprising a motor, timing gear train indicating hands and an electric switch which can be actuated at a selectable time. The set-time is selected by a selector knob connected to a shaft which moves the relative positions of a pair of gears, one of which is set manually and the other of which is driven by the timing gear train. The gears are located parallel to each other and have cams on their facing surfaces. At a predetermined relative position, the gears are forced apart by the cams to unlatch a spring-biased selector arm which closes the switch.
The timing device shown in the Polonsky patent also uses a gear train and timing gear pair in a similar manner to the Boyles timer. However, in the Polonsky device, the gears are held separated by a tooth in one gear which, at the selected time, fits into a slot in the other gear, allowing the gears to slide together. The electrical switch is integrated with the selector knob shaft and is spring-biased in an "on" position. An arm connected to the shaft latches onto one of the timing gears and holds the shaft rotated so that the switch remains open. The arm is released, allowing the shaft to rotate and to operate the switch when the gears slide together.
While the Boyles and Polonsky devices are simple and reliable, they suffer from a defect in that the switch mechanism is an integral part of the clockwork timer mechanism and, thus, they cannot use commercially-available switches. Consequently, once the mechanism has been fabricated, it is impossible to substitute electrical switches of different amperage rating or change the switch from a "normally-on" operation to a "normally-off" operation.
To remedy this defect other prior art switches were designed which could be used with commercially-available electric switches. For example, the Pomponio patent shows an electric timer which has a mechanism which can directly actuate a commercially-available microswitch. The mechanism is arranged so that the switch can easily be replaced so that switches with different characteristics can be integrated into the basic clockwork mechanism after fabrication.
The Pomponio apparatus incorporates the basic timing apparatus of the Polonsky patent, but uses a conventional microswitch operated by a cam follower. The cam follower is, in turn, actuated by cams located in a cup that is connected to the selector knob shaft. The cup can be rotated by the shaft to cause the cams to open the switch. The cup is also connected to and controlled by an arm which interacts with the timing gears in a manner similar to the arm in the Polonsky patent and holds the cup so that the switch remains open. At the selected time, the timing gears slide together, releasing the arm and allowing the cup to rotate into a position in which the cam/cam follower arrangement actuates the microswitch.
While improvements have been made to the mechanism for automatically actuating the switch, once the switch has been actuated and the associated appliance has been turned on, the timer mechanism is disengaged and no longer controls the appliance. Thus, if the user forgets to manually turn off the appliance, it will remain on indefinitely, which wastes energy and may present danger of a fire or other hazard.
Accordingly, it is an object of this invention to provide a timer mechanism which automatically deactivates the electric switch after a predetermined time lapse.
It is another object of this invention to provide a timer assembly which permits both manual and timed actuation of the switch yet automatically deactuates the switch after a predetermined period of time.
It is still another object of this invention to provide a timer mechanism with an automatic turn off which is simple and reliable.
It is a further object of this invention to provide a timer mechanism with an automatic turn off which is easy to manufacture.
It is yet another object of this invention to provide a timer mechanism with an automatic turn off which can be used with commercially-available electric switches.